Here is how George Smiley — erstwhile spy master, short-lived head of operations at London’s intelligence agency the Circus, scholar of German literature, long-suffering cuckold, and for some time the most powerful secret figure in the Cold War — is introduced on the first page of the first novel by John le Carré, 1961’s Call for the Dead: “Short, fat, and of a quiet disposition, he appeared to spend a lot of money on really bad clothes, which hung about on his squat frame like skin on a shrunken toad.” He is — his wife is known to report — “breathtakingly ordinary;” his most distinctive feature, polished again and again on the fat end of his silk tie, are his heavy, oversize spectacles.

Here is how George Smiley is introduced, after a long, conspicuous absence, on page 258 of le Carré’s Legacy of Spies, his 25th and most recent novel, published this past September: “It was the same George, just grown into the age he had always seemed to be,” reports narrator Peter Guillam, Smiley’s former right-hand man. “But George in red pullover and bright-yellow corduroys, which startled me because I’d only ever seen him in a bad suit.” He is still “owlish,” still seeming, while listening, to be “in hibernation.” “A forefinger rises absently to the bridge of his spectacles,” Guillam observes, “checking that they are still in place.”

They are. One imagines they will always be.

George Smiley is to the secret agent in English literature what Hercule Poirot is to the detective. He is the presiding hero, and the leading light. He has appeared in some capacity in a total of nine of le Carré’s novels to date: as unlikely protagonist of Call for the Dead and the small-town mystery A Murder of Quality; as ensemble player in The Spy Who Came in From the Cold and The Looking-Glass War, and later The Secret Pilgrim; as, most famously, the animating force of what is known as the Karla Trilogy, comprising Tinker Tailor Soldier Spy, The Honourable Schoolboy, and Smiley’s People; and, now, as the man whose legend looms over A Legacy of Spies, the ghost that haunts its bleak, backward-looking pages.

Given his ubiquity — Smiley has long become a fixture of the popular imagination in his homeland and beyond — it’s curious that the most consistent description le Carré affords his readers is of a man hardly worth mentioning. Often, early in a Smiley story, a character whose perspective we for the moment share will furnish us with an account of a recognizable stranger: a stout little man in macintosh and glasses will potter onto the scene, inconspicuous and otherwise nondescript, and if there is cause to remark on the fellow at all it will be to disparage him. “A podgy, ill-sighted little body in very round spectacles” is how an American newsman in Hong Kong mentions him, in The Honourable Schoolboy. He does not suspect him of significance. Nobody ever does.

Smiley has long become a fixture of the popular imagination in his homeland and beyond.

Smiley is not a glamorous hero. He does not — and this accords with le Carré’s scrupulously mundane view of espionage — find himself embroiled in dangerous pursuits, or bolt into fisticuffs in the backrooms of covert hideaways, or narrowly escape shoot outs behind enemy lines. He is equipped with no gadgets. (He is never once seen to even use a computer or a cellphone.) He isn’t tuxedo-clad or besieged by comely women. His long-anticipated scheme to thwart the nefarious head of Soviet Intelligence, the most sensational confrontation in le Carré’s fiction, climaxes in the writing of a letter. Smiley talks to several people and tells the evil Karla what he’s learned. That’s it. Game won.

And yet Smiley is also among the richest, cleverest and most fascinating characters in all of post-war fiction, a miraculous creation of inexhaustible intrigue. His exploits are exhilarating, in their own quiet way. He interrogates the enemy with the skill of a master psychologist: “The slightest careless movement on his part could have destroyed everything, but he never made it,” lamplighter Toby Esterhase gushes after watching Smiley work in Smiley’s People. He reasons and deduces with Holmesian wit: watch him weave his unassuming way through the village in A Murder of Quality, modestly gathering the necessary clues. At every turn, in every plot, he is doubted — never more than by himself. Unlike the patriots and bureaucrats who surround him, he can never be sure that the ends justify the means. That’s what makes him good, in the final estimation — and what gives le Carré’s work its provocative moral ambiguity.

In the recent film adaptation of Tinker Tailor Soldier Spy, Gary Oldman plays Smiley with what le Carré himself has described as “a hidden ferocity,” a fury lurking beneath the placid mein; it is a compelling, memorable performance. But for me — and of course for many others — the definitive portrayal will always be the one conjured, as if by magic, by Sir Alec Guinness, in both Tinker Tailor Soldier Spy and its sequel, Smiley’s People. Produced for the BBC in 1979 and 1982, respectively, this pair of six-hour specials is a rare achievement in faithful, respectful adaptation, bringing every page of the source novels to the screen almost word-for-word. And at their centre, exuding the private genius of the character, is Guinness, fully transformed.

“What you see in Alec is some kind of spiritual extension of a religious belief,” le Carré said of Guinness’s performance, many years later. “I think that his view of the role was almost as Jesuitical moderator in a sinful society.” That accounts for the quiet, almost mythical intensity the actor projects. All he needs to do is listen. Another character will tell a story, and Guinness will watch, stone silent — until, with the slightest elevation of the eyebrows and faintest trace of an ironic smile, he levels a judgement crackling with truth. In such moments you don’t feel that Guinness is responding to a cue. He is responding as Smiley: he has become the man on screen.

His exploits are exhilarating, in their own quiet way.

Le Carré has often related to journalists what happened when he elected to visit Camden Lock to watch the cast and crew of Tailor shoot the novel’s climactic scene, in which Smiley, having alerted the Mole at the top of British Intelligence to a manufactured emergency, is poised to reveal Bill Haydon as the surprise betrayer. “Here Alec was in the safe house,” le Carré remembers. “He’s in his long-johns, half made-up and it’s quite cold, he’s all wrapped up.” When suddenly he turns to le Carré: “Who do you think it’s going to be? Tinker? Taylor? It could be that nice Roy Bland.” That was how deeply Guinness had invested himself into the mind of the character. He had, le Carré says, got himself “believing that he didn’t know and that he was about to make a discovery.”

Smiley does not have a great deal to do in A Legacy of Spies, which mainly concerns the efforts of a team of less-enlightened government lawyers to investigate the vicissitudes of Circus operations past. It’s just as well: Smiley was first courted by the Circus while in college in 1928, which would put the old spy at a little over 100 by now. It isn’t difficult to understand why the Smiley legacy endures in the minds of his admirers, nor why, in these turbulent, uncertain times, we yearn to have the quiet, diligent scholar of the espionage world back on the front lines.

On the other hand, it’s difficult to imagine a more perfect ending for the character than the one le Carré provided him 40 years ago. Smiley has just witnessed the surrender of his arch-adversary Karla after the successful execution of his own elaborate plan. It’s a moment of victory, of triumph — or ought to be. Now that the end is here, our hero has doubts about the means. His conquest is profoundly bittersweet.

Here is how George Smiley — about to crest the pinnacle of his long and eminent career — is last glimpsed, on page 387 of Smiley’s People, published in 1979: “From long habit, Smiley had taken off his spectacles and was absently polishing them on the fat end of his tie, even though he had to delve for it among the folds of his tweed coat.

‘George, you won,’ said Guillam, as they walked slowly towards the car.